The Hidden Shadow
by Leah Isabella Reed
Summary: In this epic tale, heroes Percy Jackson and Harry Potter meet again. They must join together this time to fight a new evil, greater than anything they have ever faced before. I do not claim to own the Harry Potter, Percy Jackson and the Olympians, or Heroes of Olympus series.
1. Chapter 1

It was a really nice day-the sun was out, and Hogwarts Castle had never looked more beautiful. With Voldemort gone, seventeen-year-old Harry Potter could finally relax. Students had been allowed to stay at Hogwarts over summer break due to the current circumstances (many people had lost their homes, their parents, or both). Harry sat by the lake, alone.

Suddenly, someone rose out of the water. He was about Harry's age, if he had to guess, maybe a year or two younger. Harry could tell that this stranger had also fought many villains and been on the run, like him.

"Who are you?" asked the boy.

Harry was surprised. He had just defeated the most evil wizard of all time-didn't he know who he was? "I'm Harry Potter, of course."

"Of course? Am I supposed to know you?" he replied. "My name is Percy-Percy Jackson. Don't _you_ know who _I_ am?"

Harry laughed. "So we're both famous in our own world. Where are you from?"

"Manhattan, New York," answered Percy. "USA. Where are you from and where are we now?"

"I'm from here," replied Harry. "We're near London, England."

"Oh," said Percy. "So-I'm assuming we're from different worlds. I mean, you'd know about me if we weren't. What did you do?"

"I defeated the greatest evil wizard of all time," said Harry. "That was about a month ago. And I had a lot of help. What did you do?"

"A wizard," muttered Percy. "Are you a son of Hecate?"

"Who?"

"The goddess of magic. I'm the son of Poseidon, Greek god of the sea. And _I_ just defeated the first being ever to walk the Earth. Actually, she _was_ the Earth. It's a long story. And I also had a lot of help," Percy told him.

"You're right about the different worlds," said Harry thoughtfully. "How did you get here?"

"Well, I was swimming in a lake back in New York," Percy explained, "And when I came up, I was here. By the way, I can breathe underwater."

"Oh," Harry said. "Well, that explains a lot. So, you said your father is..."

"The Greek god of the sea," Percy finished. "And my mom is a regular mortal."

"A Muggle," said Harry. "You'd know if she weren't. My parents were wizards, and so am I, and so is everybody else here."

"Muggle?" asked Percy.

"That's anyone who isn't a wizard or witch," explained Harry.

They were silent for a little while.

"So, uh, what can you do?" asked Percy.

With a wave of his wand, Harry made an ant grow, then shrink, then catch on fire, then turn into a teacup.

"Cool," said Percy. Then, turning to the lake, he caused small waves, which grew a little larger. "I can summon hurricanes, too," he said. "But it takes a lot of my strength."

Suddenly, a huge shadow blocked the sun. Screams could be heard from the castle. A voice boomed:

"I AM THE DARK AND THE EVIL THAT LURKS WITHIN EVERYTHING. FOR TRILLIONS OF YEARS I HAVE SLEPT. I AM OLDER THAN TIME ITSELF. AND I HAVE BEEN FORGOTTEN. BUT I WILL BE FORGOTTEN NO LONGER! YOU HAVE SEVEN DAYS BEFORE I FULLY WAKE. PREPARE YOURSELVES. IF YOU JOIN ME, YOU WILL BE SPARED. EVERY BEING WHO DIES IS A WASTE. JOIN ME, AND YOU CAN RULE WITH ME! YOU HAVE BEEN WARNED! MWAHAHAHAHA. HAHAHAHAHAHA!"

Harry and Percy sighed in unison.

Time to save the world...again!


	2. Chapter 2

"Not again!" groaned Percy. "I _just_ beat Gaea!"

"I don't know who that is, but this shadow looks even worse," added Harry.

"It isn't from any kind of mythology I've heard of," said Percy. "And it looks like she's made of shadow." He brought out a ballpoint pen. "This is my sword, Riptide."

Harry nodded. "And I've got my wand. It looks like we're both fighters. We have a lot in common. Go figure."

"Yeah."

Suddenly, Harry had an idea. "Who are you? Or are you such a coward that you won't even show your face!"

Percy quickly caught on. "You're probably so ugly, you don't even _have_ a face!"

"HOW DARE YOU INSULT ME LIKE THIS!" the voice boomed, louder. A female human-like body materialized. "I AM, IN YOUR LANGUAGE, CHORRINA! I AM OLDER THAN CHAOS, OLDER THAN TIME ITSELF! I AM EVIL ITSELF!"

"Okay, sure, sure." Percy pretended to stifle a yawn. "Seriously? What do you even plan to do? I mean, once you destroy the world, it's kind of hard to recreate all this."

"FOOLS!" Chorrina roared. "I SHALL NOT DESTROY THE HUMAN RACE. I SHALL MAKE ALL CREATURES MY SLAVES!"

"Overdone," said Percy. "I mean, there are _so_ many books about that!"

"BUT HAS IT EVER BEEN _DONE_?"

Harry shrugged. "I don't know, I wasn't alive at the beginning of time, and you were asleep."

"NOT ASLEEP!" A new body materialized in front of her. No-two new bodies. One had a white face. One was made of dirt. Both were dead. And both scared our heroes nearly to death.

"How-" started Harry.

"Aren't they supposed to be dead?" asked Percy. Then he turned to Harry. "I'm assuming you know the white guy?"

"Voldemort," Harry said. "And you know the dirt monster?"

"Gaea," Percy said.

"THEY WERE ONLY PAWNS OF MINE!" she bellowed. "I CONTROL ALL EVIL, AND I BRING IT OUT OF EVERY BEING. I WILL RULE THE WORLD!"

"Okay." Harry was feeling kind of scared now, but he ignored the fear. "But how about you-PETRIFICUS TOTALUS!" The curse caught Chorrina off guard, but it did not immobilize her as it should have. Percy decided not to try a hurricane just yet.

"FOOLS! I AM IMMUNE TO MAGIC! NOTHING BUT YOUR WORLDS COMBINED COULD STOP ME!" And with that, Chorrina disappeared.

An idea struck Percy. "We need something to guide us."

"Yeah, we do. But who can help us?"

Percy smiled. "I know a place. Can you travel from one place to another? Preferably in about one second?"

Harry caught on. "Yeah. Where do you need to go?"

So Percy told him the coordinates of Camp Half-Blood in Long Island, New York, USA. He knew only their Oracle could help them now.

"Hold tight!" Harry yelled.

And they disappeared together.


	3. Chapter 3

After a suffocating sensation that left both boys breathless, they stopped. "Welcome," Percy said grimly, "to Camp Half-Blood."

The whole place was in ruins. It was a test, Harry realized, of the power of Evil itself. No one was outside. It looked like there had been a few dozen cabin-like buildings. All but one were in ruins. Only two other buildings remained.

A centaur walked up-or, more accurately, galloped up. His face was grim. "Who is this?" he asked Percy. "He isn't a mortal or a half-blood."

"Actually, I am a half-blood," Harry said. "But I assume we're talking about different definitions here…"

"Yes, I'm sure we are," agreed the centaur. "I am Chiron. I train heroes. Everyone else is at the dining pavilion."

"I'm Harry Potter. I'm a wizard."

"Oh, I see," murmured Chiron. "But why are you here?"

"We need to speak to Rachel," Percy explained.

"This isn't really a quest, you know."

"Maybe, but we really need a prophecy."

That moment, Rachel came down. "I heard my name," she said. "Do you guys need a prophecy?"

"Yeah, we do." Percy grinned sheepishly.

"Okay, then. Um, I'm not sure how this is going to work." She turned to Harry. "You're a half-blood, but neither of your parents are immortal."

"Yeah, different kind of half-blood," Harry said.

"Now, which of you is the leader of this quest?" asked Chiron.

"I am," said Percy and Harry at the same time. "Okay, he is."

"Okay, you then," said Harry. "I assume you've done this before?"

Suddenly, Rachel's face glowed green. "What's going on?" asked Harry."

"Don't worry, this is normal under these circumstances," Percy assured him.

 _Two different heroes Evil must fight,_

 _Their worlds must they reunite,_

 _None will fall to death's hand,_

 _If shadows are found from the Silent Lands._

"What was _that_ all about?" asked Harry, bewildered.

"That was a prophecy," explained Chiron.

Rachel blinked three times, but she remained standing. "It was? Oh. Well, at least I didn't fall over this time."

"So, we have to go to the Silent Lands. Okay. Where might these be?" asked Percy.

Chiron grimaced. "I do not wish to send either of you there, but it appears to be necessary. They are a chain of islands off of Russia. There is a landmark from an ancient tribe of some sort. They call it the _Τάρταρα Σελήνη_."

"Tartarus Moon," Percy translated effortlessly. Then he shuddered. "I hope that place is nothing like Tartarus itself."

"No time to waste," said Harry. "We'd better go now. I've never gone that far before, but I'll try. I don't think we'll get Splinched."

"Splinched?"

"That's when part of you gets left behind," he explained. "Now let's go."

"Wait...LEFT BEHIND?" Percy yelled.

But his cry was lost as they disappeared.


	4. Chapter 4

For a second, Harry was worried that he _wouldn't_ land.

They were traveling longer than usual, he felt sure of it. But, as always, they arrived the second he thought he would suffocate.

"For the record, I hate-" Percy frowned. "-uh, whatever this is!"

"Apparation," Harry told him, "and so do I. Unfortunately, it's the best way to travel long distances."

Percy searched for the landmark. It took him a while to find the pile of rocks that resembled a black moon. "Come here," he called. "I think I've found it!"

But Harry couldn't come. He was too busy fighting a monster. "Stupefy!" he yelled. "Petrificus totalus!" The spells did nothing to the huge four-eyed beast. Percy remembered what Chorrina had said: _nothing but your worlds combined could stop me!_ And Rachel's prophecy: _Their worlds must they reunite._

Percy dashed over and yelled, "Hey, can you cast a spell that makes a ton of water?"

"We're on an island! There's plenty of water!"

"It has to be _magic_ water!"

"Okay then-AGUAMENTI!" Water blasted out of Harry's wand. Percy brought it toward himself and summoned a hurricane. Together, they blasted the monster out of the sky.

"Okay," said Percy, "is it really that easy?"

"Well _now_ is isn't!" Harry replied. "Look, I think there's another-AAAAAGH!" A beam of light-Percy guessed it was a spell-hit Harry in the stomach, and he fell over. He didn't appear hurt but was obviously in pain. But he got back up. "Cruciatus Curse," he muttered to himself. "But who…"

"YOU DARE FIGHT MY MINIONS?" a voice boomed.

Percy fake-groaned. "Back so soon? You _just_ got back from terrorizing us."

"I AM THE FIRST EVER BEING, HAVE YOU FORGOTTEN? I DO NOT NEED _REST_! AND BE WARNED-YOU MAY HAVE DEFEATED MY FIRST SURPRISE. BUT MY OTHER CHILDREN WILL BE MUCH WORSE. YOU WILL NEVER REACH THE SILENT LANDS!"

"Wait...aren't we in the Silent Lands?" asked Harry.

"NO, YOU FOOL! YOU ARE IN AUSTRALIA!" she disappeared.

"How are we in Australia?" asked Percy. "You took us to Russia, I thought."

"She must be sending me off course," Harry replied. "This is going to be a pain."

"Are there any other quick ways of travel?" asked Percy.

"Well...there is one way. Are you cool with flying?" asked Harry.

"Yeah," Percy replied. "I mean, my girlfriend will kill me if I get blasted out of the sky and my dad-god of the sea-has a huge rivalry with Zeus-his brother and the god of the sky. But I think he'll be to preoccupied to notice."

"Okay then." _Accio two Firebolts!_ Harry thought. He knew he had to master nonverbal spells, and now was as good a time as any."

A minute later, two Firebolts-one of which Harry immediately recognized as his own-zoomed into view. "Are you sure about this?" Percy asked as they climbed on.

"It's fine," Harry assured him. "Just hold on tight." And with that, he took off, with Percy right behind.


	5. Chapter 5

Percy was sure that Zeus would understand why Harry was flying to Russia. After all, Percy was just trying to save the world. But just in case, he prayed to Zeus. Hey, you can't be too careful, right?

They zipped through the sky. Harry had enchanted Percy's broomstick to follow his, as Percy was new to flying. They flew for hours, silently, until Harry stopped at a river. He muttered an incantation and said, "Okay, now we're in northern China. We're closer. Let's take a break-we'll need rest."

But, yet again, something stopped them. This time, it was a person. Neither boy knew him. "You dare try to stop Chorrina?" he asked. His voice wasn't loud, but it was commanding and kind of scary. "I am Hagfla. And I am going to kill you."

"Petrificus totalus!" Harry shouted. The spell did nothing. "Sectumsempra!" Nothing.

"You must become what you are not to defeat me," said Hagfla. "Together."

Percy glanced at Harry, remembering that time in Tartarus when he and Annabeth met Akhlys. To become what he was not…

Harry was thinking the same thing, remembering just a few months ago,that goblin. He wasn't sure if he could do this, though...

"Are you thinking…" Percy began.

"I think so, and I hope we're wrong."

"I don't want to do this…"

"But we have to. He's evil, and he _will_ kill us if we don't-" Harry broke off.

Percy concentrated really hard. Hagfla's face turned red. This time, when Harry yelled "Sectumsempra!" his face practically broke open. Hagfla clearly hadn't thought that Harry and Percy would do it. He disappeared, leaving no trace behind.  
"Let's get some sleep," suggested Percy.  
"Good idea," replied Harry, who put up a few protective enchantments. "I can't really do anything about food, though…"  
"It's fine," said Percy. "I'll ask Demeter for something, maybe."

They lay down by the river and fell asleep almost instantly.


	6. Chapter 6

_**Sorry about the long wait, I've been super busy. But now it's summer, so I should have plenty of time!**_

Percy didn't have any dreams, which was strange. Maybe everybody was too scared to bother with demigod nightmares. Percy hoped not-he didn't miss the dreams, but if the gods-and the Titans, and all the other evil mythological figures-could do nothing (just admit it, Zeus) then what chance did he and Harry have? The sky was dark. He fell back asleep-or so he thought.

Harry sat bolt upright. Then he noticed Percy. He had a sort of black glow around him. Harry was certain that wasn't normal, even for demigods.

Percy jerked and twisted, like he was trying to get a wrestler off of his back. Harry realized that Percy was throwing off a curse or something else. "YOU-get off me!-NEVER-stop it!-ARRIVE-what the-SILENT-help me out here!-LANDS…" Harry pointed his wand at Percy and muttered " _Finite Incantatem,"_ but beyond that, there was not much he could do. Percy's eyes flickered between his usual blue-green and solid black, and his voice was like a Muggle radio with a _lot_ of static.

Harry hated to Stun his friend, but it was obviously the only thing he could do. Percy couldn't throw off whatever this was-it clearly wasn't an Imperius Curse-forever. Concentrating as hard as he could. "STUPEFY!" he yelled. Percy fell backward.

Harry rushed over and woke up Percy. "You all right?" he asked.

"Yeah," said Percy, sitting up. "That was weird. It was like eidolons again...but it couldn't be, they swore they wouldn't…"

"I'm guessing that's something else I'll learn about." Harry made a mental note to move next time before sleeping.

Then-surprise, surprise-Chorrina appeared. "YOU HAVE DESTROYED MY-" she made a series of noises-"AND FOR THAT YOU SHALL PAY!"

"Grab the Firebolt! I'm trying Apparation!" Harry called. And once again they were off.

It was dark when they landed. Chorrina was nowhere to be found. Percy instantly found a rock formation shaped like a moon. Harry cast a spell.

"Well," he told Percy, "We're here."


	7. Chapter 7

**Hey, guys. I just want to say-thank you so much for reading! This probably isn't publishing quality, but you guys read it anyway.**

 **Hope you like the ending!**

Instantly, everyone came out of nowhere. There were too many evil beings to count. Satyrs and centaurs. Beasts and people. Gods and Titans. Some had risen from the dead. Some were well and alive. There were good guys and bad guys. Harry's and Percy's shouts could barely be heard over the uproar.

"Dumbledore! Is that really you?"

"Styx, it's Kronos! Wait, no, that's Luke!"

"What the-[Censored], it's Bellatrix Lestrange!"

"Wait-there are two Lukes! Which one is Kronos?"

Soon everyone knew who was who and there was an all-out battle. "Styx and stones may break my bones, but spells can never hurt me!" yelled some Death Eater. Then someone yelled "Confringio!" _Bye-bye, Death Eater,_ thought Harry. Spells. Objects. Water. Wind. Grapes. Wait...grapes?

"Hey, Dionysus!" shouted Percy as an enormous guy was strangled.

Then it was really chaos. Things and people disintegrated as they died. The battle lasted for hours. And then Ron and Hermione were there, and the demigods from the Argo II and Nico, Reyna, Hedge, Grover, and Thalia. But at the end of it all, it was only the good that remained.

"Dad…" a man was standing in front of Harry-his father.

"This is awkward," muttered Percy.

"Harry, I never thought I'd see you again. But I must go."

Harry knew it was true. He knew better than to be tempted. "I know."

The dead dematerialized. The gods left for Olympus. Minor gods left, too-except for Hecate.

"NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!" wailed Chorrina as she rose up toward the sky. "MY KINGDOM!" And then she was gone.

Then Hecate pulled herself, Harry, and Percy out of time. "You know what to do," she said.

"Obliviate Maximus!" Harry yelled to the frozen world as Percy summoned Lethe water from the depths of the Underworld and created a mist. Then they came back to reality.

Everyone had forgotten the past 24 hours. It was, according to them, the same day it had been when Chorrina first showed up. Everyone, that is, except for Percy and Harry. But that was fine by them.

All both boys wanted was a shot a normal.


End file.
